Numerous techniques exist to vary the power of a transmitter or transceiver operating within a communication system. For example, it is known that battery powered transceivers (subscriber units) may be instructed by a fixed station (i.e., a base unit or a repeater) to increase or decrease their transmitter power based on the strength of the received signal by the base. Accordingly, upon receipt of an appropriate command code from the fixed station, the battery powered transceiver adjusts its transmitter power (up or down) by a predetermined amount in accordance with the received signal strength measured at the fixed station. In this way, the operational life of the battery power subscriber units may be increased by permitting transmissions at reduced power when the battery powered subscriber units are near the fixed station.
In communication systems that measure the received signal strength for cutting back transmitter power of the subscribers units, the effects of receiver noise power are not taken into consideration. Generally, the assumption is made that the receiver noise floor is constant. However, the receiver noise floor may be effected by such external noise sources as adjacent channel transmitter side band noise and intermodulation distortion which may substantially increase the receiver noise floor. When the receiver noise floor is increased the received signal strength alone may not be sufficient to determine required power adjustment in the subscriber unit. For instance, under these circumstances the communication units must increase the transmitter power to accommodate for the increased noise level and to increase by the received signal to a level above the noise floor which provides uninterrupted communication. The received signal strength may go below the noise floor without the subscriber unit having any information to increase the received signal strength above the noise floor.